There has been known a single facer which forms a single-faced corrugated board by providing a corrugating medium with a corrugation having a predetermined pitch size, and providing the medium with a liner upon the crests of the corrugations using a suitable adhesive. In such a single facer, a gluing unit for applying a glue to the corrugating medium is indispensable. The gluing unit is basically composed of an applicator roll, a doctor roll and a glue pan.
In the above gluing unit, the glue disposed within the glue pan is taken up by means of the applicator roll and the glue disposed upon the applicator roll surface is leveled by means of the doctor roll so as to form a uniform glue layer. The glue is then applied to the crests of the corrugated medium, having a predetermined type of flute formed by means of predetermined fluted rolls, through means of the applicator roll. The thus glued corrugated medium is bonded by means of a predetermined amount of pressure with a liner so as to form a single-faced corrugated board.
In the gluing unit, if the zone of the glue disposed upon the applicator roll has a width wider than the width of the corrugated medium during transfer of the glue from the applicator roll to the corrugated medium, the glue disposed upon the applicator roll is undesirably transferred to the fluted rolls. In order to prevent such undesired glue transference to the fluted rolls, the gluing unit is designed to have a pair of dam plates (generally referred to as "glue dams") disposed within the glue pan so as to be movable toward and away from each other along the axis of the applicator roll so as to allow the glue confined between the glue dams to be taken up by means of the applicator roll. Accordingly, by adjusting the axial distance defined between the glue dams depending upon the width of the corrugated medium, the glue is permitted to be deposited upon the applicator roll only within a zone or region having a width corresponding to the width of the corrugated medium.
In this context, while corrugators are designed to be operated at a high rate of speed in order to improve productivity of corrugated board sheets in the corrugator industry, the following problem has arisen with respect to the speed of the production line. To describe the problem in detail, with the high-speed operation of the single facer, the applicator roll also undergoes high-speed rotation, whereby the amount of glue to be taken up by means of the roll is increased. The surplus glue scraped off or removed from the applicator roll by means of the doctor roll does not drop back toward the glue pan but stays within the vicinity of the zone where the two rolls are brought into contact with each other, as a result of the high-speed rotation of the applicator roll, and consequently the surplus glue overruns the glue dams and spreads outwardly along the axis of the applicator roll. Consequently, the glue is spread upon the applicator roll over an area which is wider than the width of the corrugated medium, and thus, the fluted rolls are contaminated by means of the overflowing glue portions transferred thereto.